The U.S. economy is still at risk and the recovery is fragile, but Federal Reserve Chairman Ben Bernanke, testifying on Capitol Hill Thursday, refused to be pinned down on what additional steps can be taken to spur economic growth.

Investors are closely watching Bernanke for signs of additional stimulus, or a third round of quantitative easing, known as QE3, to boost the sagging economy. Earlier this week three other Federal Reserve officials said the Fed may need to act to support economic growth.

Meanwhile, fixed rate mortgages had the sixth straight week of record lows. Freddie Mac reported the average U.S. rate on 30-year mortgage dropped to a record-low 3.67 percent while the 15-year rate dropped to 2.94 percent.

During his testimony, Bernanke again said the Federal Reserve was prepared to act to boost the economic recovery and stressed the importance of the nation's long-term fiscal stability.

"I don't think we're in a Greek situation," Bernanke said in answer to a question about whether the U.S. economy is headed toward Greece's debt issues. Greece may have to exit the euro if it's unable to borrow more to finance its debt.

"That being said, I don't think we should be complacent," Bernanke said.

After hearing Janet Yellen, vice chair of of the Fed's board of governors, and Dennis Lockhart, President of the Federal Reserve Bank of Atlanta, comment this week about possible Fed action, investors expected further statements from Bernanke.

"Everyone thought he would deliver more but he didn't," Gibbs said.

Stocks had their biggest day of the year on Wednesday on speculation the Fed would act and that Europe might be getting its fiscal house in order. Futures were higher Thursday morning after yesterday's rally and the overnight report that China cut its benchmark lending rates for the first time since 2008.

The Dow Jones Industrial Average was the only index that closed up for the day. It closed up 0.37 percent to 12,461. The S&P 500 closed slightly lower by 0.01 percent to 1,315 while Nasdaq closed down 0.48 percent to 2,831.

"It doesn't take away the positive move we had the last few days but it does take away a little bit from the rally's luster," Gibbs said of the market's close.

The S&P 500 rose about five points when the Bernanke speech was released, but gave back most of that improvement during the Q&A after his testimony.

LeBas said it seemed clear that the Federal Reserve's monetary policy-making group, the Federal Open Market Committee (FOMC), is leaning towards additional stimulus at their upcoming meetings.

Bernanke said "at this point I really can't say anything is completely off the table."

"The idea of 'standing ready to act,' which was Bernanke's central message, is meaningless if the Fed allows Operation Twist to expire at the end of June," LeBas said.

The Federal Reserve announced a debt swap, dubbed Operation Twist, in September 2011, selling $400 billion of long-term securities for an equal amount of shorter-term instruments.

"For months, policymakers have been arguing that, if things get worse, they'll need to add more stimulus," LeBas said. "Now, judging by the data, things are worse, and it follows that the Fed is likely to attempt to do more to boost economic output and stave off deflation risk."

While economic growth has continued at a "moderate rate so far this year" and "appears to be poised to continue at a moderate pace over coming quarters," Bernanke said in his testimony that some factors that have restrained the recovery persist.

Those include households and businesses more cautious to spend and invest as well as a depressed housing market.

"With unemployment still quite high and the outlook for inflation subdued, and in the presence of significant downside risks to the outlook posed by strains in global financial markets, the FOMC has continued to maintain a highly accommodative stance of monetary policy," Bernanke said during his testimony.

The target range for the federal funds rate remains at 0 to 1/4 percent, and the FOMC still anticipates that economic conditions are likely to warrant "exceptionally low levels of the federal funds rate" at least through late 2014, he said in his speech.

Members of Congress pressed Bernanke about whether the Federal Reserve was doing too much to interfere with the economy while others pressed him to act further.

"Monetary policy is not a panacea," Bernanke said during the Q&A, adding that "it would be much better" to have a broad-based policy effort implemented by Congress.

"I would feel much more comfortable if Congress would take some of this burden from us and address these issues," he said.